The nature of the apparently isozymic forms and subunits of pyridoxamine (pyridoxine) 5'-phosphate will be studied. A sensitive and specific fluorometric assay based on N-(5'-phospho-4-pyridoxyl) amines as substrates will be developed to facilitate assays, especially for assessment of low activities in the blood of riboflavin-deficient mammals. Riboflavin-binding proteins will be more fully characterized, and the specificity and nature of flavin binding will be related to flavin oxidation-reduction potential altered as a consequence of binding. Further investigations will be made of flavinyl peptides related to the active site of mitochondrial monoamine oxidase. In particular, the nature of the tyrosyl-flavin association and the effect of this superimposed on the electronic perturbation caused by the thioether link to the cysteinyl moiety will be determined. The biosynthesis of mitochondrial flavoproteins will be investigated in hepatic mitochondria of riboflavin-deficient rats. Additional work is planned to delineate the biochemical sequalae resulting in the formation of aberrant, giant mitochondria in deficient animals.